Droplet discharge device, head cleaning method, and program

Abstract

To provide a droplet discharge device, a head cleaning method and a program that can restrict deterioration in quality of an image to be formed, by properly cleaning away mist adhering to a nozzle surface according to a charge amount of a recording medium.SOLUTION: A droplet discharge device comprises: an image formation unit 24 which discharges droplets from a nozzle of a droplet discharge head onto a conveyed recording medium M in order to record an image; a head cleaning device 40 for cleaning the droplet discharge head; and a control device 50. The control device 50 controls a cleaning operation of the head cleaning device 40 according to a charge amount of the recording medium M.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a droplet ejection device, a head cleaning method, and a program. [Background technology]

[0002] A droplet ejection device that ejects droplets from nozzles in a droplet ejection head onto a recording surface of a recording medium to form an image is known. In such a droplet ejection device, droplets are ejected from the nozzles at appropriate timing based on image data.

[0003] In such droplet ejection devices, if image formation is performed while the mist adhering to the nozzle surface is left as it is, image quality will deteriorate due to deflected or missing droplet ejection, so it is necessary to clean the nozzle surface of the droplet ejection device.

[0004] Therefore, for example, Patent Document 1 describes an inkjet recording apparatus that predicts the state of the nozzle surface based on various conditions and controls cleaning of the nozzle surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-101630 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the invention of Patent Document 1 does not take into account the charge amount of the recording medium when controlling the cleaning of the nozzle surface. FIG. 4A is a graph showing the relationship between the charge amount of the recording medium and the amount of mist adhering to the nozzle surface and the amount of satellites landing on the recording medium. FIG. 4B is a diagram showing the status of mist adhering to the nozzle surface and the status of satellites adhering to the recording medium for each charge amount of the recording medium. In FIG. 4A, the horizontal axis represents the charge amount of the recording medium, and the vertical axis represents the number of mist adhering to the nozzle surface or the number of satellites landing on the recording medium. As shown in FIGS. 4A and 4B, the amount of mist adhering to the nozzle surface increases dramatically as the charge amount of the recording medium increases. In the invention of Patent Document 1, the nozzle surface is not cleaned according to the charge amount, which can result in a decrease in the quality of the formed image.

[0007] Furthermore, if the frequency or intensity of cleaning of the nozzle surface is increased unnecessarily, problems arise such as increased downtime, reduced productivity in image recording processing, and wear on the nozzle surface, causing deterioration of the droplet ejection head.

[0008] The present invention has been made in view of the above circumstances, and its object is to provide a droplet ejection device, a head cleaning method, and a program that can more appropriately clean mist that has adhered to the nozzle surface and prevent a decrease in the quality of the formed image. [Means for solving the problem]

[0009] In order to solve the above problems, the invention described in claim 1 is a droplet ejection device, an image forming unit that records an image by ejecting droplets from nozzles of a droplet ejection head onto a conveyed recording medium; a head cleaning device that cleans the nozzle surface of the droplet ejection head; a control unit, The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount of the recording medium.

[0010] The invention described in claim 2 is the droplet ejection device described in claim 1, The control unit controls the cleaning operation of the head cleaning device in accordance with the amount of charge on the recording medium before the image forming unit ejects droplets onto the recording medium.

[0011] The invention described in claim 3 is the droplet ejection device described in claim 2, a surface potential meter for measuring a surface potential of the recording medium on an upstream side of the image forming unit in a conveyance direction; and an acquisition unit that acquires the charge amount from the surface potential measured by the surface potential meter.

[0012] The invention described in claim 4 is the droplet ejection device described in claim 1, The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount set for each type of recording medium.

[0013] The invention described in claim 5 is the droplet ejection device described in claim 1, a media sensor for measuring physical properties of the recording medium; The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the measurement result of the media sensor.

[0014] The invention described in claim 6 is the droplet ejection device described in claim 1, a static elimination device that eliminates static from the recording medium; and a static elimination performance measuring device that measures the static elimination performance of the static elimination device, The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the measurement result of the static elimination performance measuring instrument.

[0015] The invention described in claim 7 is the droplet ejection device described in claim 1, an image reading unit that reads the image formed on the recording medium by the image forming unit; The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the reading result of the image reading unit.

[0016] The invention described in claim 8 is the droplet ejection device described in claim 1, a measuring unit for measuring temperature information and / or humidity information; The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the measurement result of the measurement unit.

[0017] The invention described in claim 9 is the droplet ejection device described in claim 1, a detection unit that detects the amount of mist adhering to the nozzle surface, The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount and the detection result of the detection unit.

[0018] The invention described in claim 10 is the droplet ejection device described in claim 9, The detection unit is a camera or a sensor.

[0019] The invention described in claim 11 is the droplet ejection device described in claim 1, The control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount and at least one of the operating time of the droplet ejection device, the number of images formed, image formation conditions, and liquid consumption amount.

[0020] The invention described in claim 12 is the droplet ejection device described in any one of claims 1 to 11, The control unit controls the timing at which the head cleaning device cleans the nozzle surface as the cleaning operation.

[0021] The invention described in claim 13 is the droplet ejection device described in any one of claims 1 to 11, The control unit controls the strength of cleaning the nozzle surface by the head cleaning device as the cleaning operation.

[0022] The invention described in claim 14 is the droplet ejection device described in any one of claims 1 to 11, The control unit controls the number of times the head cleaning device cleans the nozzle surface as the cleaning operation.

[0023] The invention described in claim 15 is the droplet ejection device according to any one of claims 1 to 11, The head cleaning device includes a plurality of types of head cleaning means, The control unit controls which of the plurality of types of head cleaning means is to be used for the cleaning operation.

[0024] The invention described in claim 16 is an image forming unit that records an image by ejecting droplets from a droplet ejection head onto a conveyed recording medium; a head cleaning device that cleans the nozzle surface of the droplet ejection head, The method further includes a control step of controlling the cleaning operation of the head cleaning device in accordance with the amount of charge on the recording medium.

[0025] The invention described in claim 17 is a program, an image forming unit that records an image by ejecting droplets from a droplet ejection head onto a conveyed recording medium; a head cleaning device that cleans the nozzle surface of the droplet ejection head; The head cleaning device functions as a control unit that controls the cleaning operation of the head cleaning device in accordance with the amount of charge on the recording medium. [Effects of the Invention]

[0026] According to the present invention, mist adhering to the nozzle surface can be properly cleaned off, and degradation of the quality of the formed image can be suppressed. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 2 is a side cross-sectional view of the droplet ejection device. [Figure 2] FIG. 2 is a block diagram of a droplet ejection device. [Figure 3]10 is a flowchart of a nozzle surface cleaning process. [Figure 4A] 10 is a graph summarizing the relationship between satellite droplets that land on a recording medium and mist that adheres to a nozzle surface of a droplet ejection device according to the amount of charge on the recording medium. [Figure 4B] 10A and 10B are schematic diagrams of a nozzle surface of a droplet ejection device and a recording medium according to the amount of charge on the recording medium. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, droplet ejection devices according to embodiments of the present invention will be described in detail with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. In the following description, components having the same functions and configurations will be assigned the same reference numerals, and their description will be omitted.

[0029] [Overall configuration of droplet ejection device] Fig. 1 is a side cross-sectional view showing the schematic configuration of an inkjet recording apparatus 1, which is one embodiment of a droplet ejection device of the present invention. Fig. 2 is a block diagram showing the functional configuration of the inkjet recording apparatus 1. The inkjet recording apparatus 1 includes a paper feeder 10, an image forming apparatus 20, a paper discharger 30, a head cleaning apparatus 40, and a control device 50. The inkjet recording apparatus 1 forms an image by ejecting ink droplets onto a recording medium M conveyed from the paper feeder 10 using the image forming apparatus 20, and then discharges the recording medium M to the paper discharger 30.

[0030] (Paper feeder) The paper feeding device 10 includes a paper feeding tray 11 and a paper feeding section 12. The paper feeding tray 11 stores recording media M. The paper feeding section 12 conveys the recording media M to the image forming device 20 under the control of the control device 50.

[0031] The recording medium M is not limited to paper such as plain paper or coated paper. Various media can be used as the recording medium M, such as fabric or sheet-like resin, as long as ink droplets that land on the surface can be fixed thereto. Also, while Fig. 1 illustrates a paper feed device 10 having one paper feed tray 11, the present invention is not limited to this, and the paper feed device 10 may have multiple paper feed trays 11 that store multiple types of recording media M, respectively.

[0032] (Image forming device) {Body} Image forming apparatus 20 includes multiple types of cylinders 21 for transporting recording medium M. In this embodiment, the multiple types of cylinders 21 include A cylinder 21a, A cylinder hold-down roller 21b, recording medium hold-down roller 21c, and triple cylinder 21d. Cylinders 21 sandwich recording medium M to transport recording medium M in the transport direction.

[0033] The image forming apparatus 20 also includes a static eliminator 22 , a surface potential meter 23 , an image forming section 24 , a fixing section 25 , an image reading section 26 , and a transport roller 27 .

[0034] {Static eliminator} The static eliminator 22 is provided upstream in the transport direction from the image forming unit 24. The static eliminator 22 is a static eliminator that removes the voltage applied to the recording medium M. For example, the static eliminator 22 removes the electric charge by clamping the recording medium M between conductive rollers connected to the ground (GND).

[0035] The static eliminator 22 also includes a static elimination performance measuring device 22a that measures the static elimination performance of the static eliminator 22 by acquiring, for example, the current values ​​of the recording medium M on the upstream and downstream sides of the static eliminator 22 in the transport direction.

[0036] {Surface electrometer} The surface electrometer 23 is provided upstream of the image forming unit 24 in the transport direction and in the vicinity of the image forming unit 24. The surface electrometer 23 detects the surface potential of the recording medium M. The surface potential of the recording medium M detected by the surface electrometer 23 is transmitted to the control device 50.

[0037] {Image forming section} The image forming unit 24 forms an image on the recording medium M transported by the cylinder 21 (triple cylinder 21d). In this embodiment, the image forming unit 24 includes a plurality of head units each consisting of a plurality of inkjet heads, as shown in FIG. 1. Each head unit ejects ink of a corresponding color from a nozzle opening facing the transport surface of the triple cylinder 21d at an appropriate timing according to the rotation of the triple cylinder 21d holding the recording medium M, thereby forming an image. The colors of ink ejected by the head units are, for example, four colors: Y (yellow), M (magenta), C (cyan), and K (black), but are not limited to these.

[0038] The head unit is positioned so that its nozzle openings are spaced a predetermined distance from the conveyance surface of the triple cylinder 21d. Under the control of the control device 50, the head unit moves to a position where its nozzle surface faces the head cleaning device 40 during a nozzle surface cleaning process, which will be described later.

[0039] {Fixing part} The fixing unit 25 is provided downstream of the image forming unit 24 in the transport direction. The fixing unit 25 fixes the image formed on the recording medium M by the image forming unit 24. The fixing unit 25 is, for example, an energy ray irradiation unit. Specifically, the fixing unit 25 includes a light emitting unit arranged across the width of the triple cylinder 21d in the direction perpendicular to the transport surface. The light emitting unit irradiates the transported paper P with energy rays such as ultraviolet rays under the control of the control device 50. This hardens and fixes the ink on the recording medium M.

[0040] {Image reading unit} The image reading unit 26 is disposed downstream of the fixing unit 25 in the transport direction so as to be able to read the image forming surface, which is the surface of the recording medium M. The image reading unit 26 is, for example, a line sensor. The image reading unit 26 reads the image forming surface of the recording medium M within a predetermined reading range and transmits the captured image data to the control device 50.

[0041] {Transport roller} Conveying roller 27 is provided downstream in the conveying direction from image reading unit 26. Conveying roller 27 conveys recording medium M, which has passed through image forming unit 24 and fixing unit 25 and been handed over from triple cylinder 21d, to paper discharge device 30.

[0042] (Paper output device) The paper discharge device 30 stores the recording medium M discharged from the image forming device 20 until the user collects it. The paper discharge device 30 includes a plate-shaped paper discharge tray 31. Note that the paper discharge device 30 may include multiple paper discharge trays 31, similar to the paper feed device 10. In this configuration, the paper discharge device 30 appropriately controls the storage destination of the recording medium M in accordance with instructions from the control device 50 according to the image formation conditions of the image forming device 20.

[0043] (Head cleaning device) The head cleaning device 40 removes ink mist adhering to the nozzle surface of the inkjet head. The head cleaning device 40 includes, for example, a plurality of types of head cleaning means.

[0044] For example, a cleaning blade is one example of the head cleaning means provided in the head cleaning device 40. The cleaning blade is a metal member made of, for example, stainless steel, which is resistant to corrosion by ink, and has a bent rectangular plate shape that protrudes from the nozzle face. When the head unit moves, the cleaning blade does not come into contact with the nozzle face, but only comes into contact with the ink mist on the nozzle face, thereby scraping off relatively large ink mist.

[0045] An example of the head cleaning means provided in the head cleaning device 40 is a cleaning wipe. The cleaning wipe is, for example, an absorbent sheet or the like bridged between a pair of rollers that includes multiple rollers. Every time the sheet or the like comes into contact with the nozzle face to wipe off ink, the wiping surface is taken up by the pair of rollers, and the other surface forms the wiping surface.

[0046] An example of the head cleaning means provided in the head cleaning device 40 is a cleaning roller. The cleaning roller is, for example, a web roller or a sponge roller, in which a web layer or an elastic layer is formed on a metal core. The cleaning roller wipes off ink by rotating in contact with the nozzle surface under the control of the control device 50.

[0047] The head cleaning device 40 may also include a liquid ejection unit that ejects liquid such as water or a cleaning liquid to soften the ink. Alternatively, the cleaning blade, cleaning wipe, and cleaning roller may be configured to be immersed in the liquid as needed.

[0048] The head cleaning means provided in the head cleaning device 40 is not limited to one or more of the above, and any known configuration may be adopted as appropriate.

[0049] (Control device) The control device 50 controls the operation of each device that constitutes the inkjet recording apparatus 1. The control device 50 includes a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory).

[0050] The CPU executes various types of arithmetic processing. The CPU also controls the overall operation of the inkjet recording apparatus 1. The RAM provides the CPU with working memory space and stores temporary data. The ROM stores various control programs executed by the CPU, setting data, etc. Note that rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or flash memory may be used instead of the ROM.

[0051] [Nozzle surface cleaning process] The nozzle surface cleaning process by the head cleaning device 40 in the inkjet recording apparatus 1 described above will be described with reference to the flowchart in Fig. 3. In the nozzle surface cleaning process, the control device 50 controls the operation of the head cleaning device 40 in accordance with information relating to the charge amount of the recording medium M. More specifically, the control device 50 determines whether or not to clean the nozzle surface with the head cleaning device 40 in accordance with the information relating to the charge amount of the recording medium M, and if so, how to clean it.

[0052] The control device 50 acquires information regarding the charge amount of the recording medium M (step S101). The information regarding the charge amount includes a measured value or an estimated value of the charge amount of the recording medium M, as well as information for correcting the estimated value. In this embodiment, the control device 50 acquires the measured value of the charge amount before the image forming unit 24 ejects ink droplets onto the recording medium M from the surface electrometer 23. The control device 50 then calculates a cumulative value of the measured values ​​of the charge amount of the recording medium M and controls the cleaning operation of the head cleaning device 40 based on the cumulative value. In this way, the control device 50 functions as an acquisition unit that acquires the charge amount from the surface potential measured by the surface electrometer 23.

[0053] Incidentally, the recording medium M becomes charged due to contact, friction, and peeling between the recording medium M and each other or with conveying members such as the cylinder 21. Therefore, in this embodiment, the above-mentioned "before the image forming unit 24 ejects ink droplets onto the recording medium M" may be any time between the placement of the recording medium M on the triple cylinder 21d and image formation by the image forming unit 24. With this configuration, the nozzle surface can be cleaned more appropriately than, for example, when the amount of charge on the recording medium M in the paper feed device 10 is referenced. In particular, it is more preferable to clean the nozzle surface immediately before the image forming unit 24 ejects ink droplets onto the recording medium M.

[0054] The control device 50 determines whether or not cleaning of the nozzle surface by the head cleaning device 40 is necessary based on the information regarding the charge amount of the recording medium M acquired in step S101 (step S102). If it is determined that cleaning of the nozzle surface is not necessary (step S102; No), the control device 50 ends the nozzle surface cleaning process.

[0055] If it is determined that cleaning of the nozzle surface is necessary (step S102; Yes), the control device 50 determines the mode of the nozzle surface cleaning operation by the head cleaning device 40 based on information regarding the charge amount of the recording medium M (step S103).

[0056] The cleaning operation mode determined by the control device 50 includes the timing, intensity, and number of times of the cleaning operation. Furthermore, as described above, if the head cleaning device 40 is equipped with multiple types of head cleaning means, it also includes which head cleaning means to use for cleaning. Specifically, for example, if the recording medium M has a high charge amount, it is expected that a large amount of ink mist will adhere to the nozzle surface. Therefore, the control device 50 determines the cleaning operation mode of the head cleaning device 40 so that the blade scrapes off relatively large ink mist.

[0057] The control device 50 controls the head cleaning device 40 in accordance with the determined mode to clean the nozzle surface (step S104). After cleaning the nozzle surface, the control device 50 ends the nozzle surface cleaning process.

[0058] [Effects of the embodiment] As described above, the inkjet recording apparatus 1 according to this embodiment includes an image forming unit 24 that records an image by ejecting droplets from the nozzles of a droplet ejection head onto a conveyed recording medium M. The inkjet recording apparatus 1 also includes a head cleaning device 40 that cleans the droplet ejection head, and a control device 50. The control device 50 controls the cleaning operation of the head cleaning device 40 in accordance with information related to the charge amount of the recording medium M.

[0059] According to this configuration, it is possible to prevent a decrease in the quality of the image to be formed by appropriately cleaning the mist adhering to the nozzle surface according to the charge amount of the recording medium M. Furthermore, according to this configuration, it is possible to predict the contamination of the nozzle surface of the inkjet head according to information relating to the charge amount of the recording medium M that can be obtained in advance. Therefore, compared to a configuration in which the state of the nozzle surface is detected and then cleaned, it is possible to prevent a decrease in the quality of the image to be formed on the recording medium M before it occurs, and to prevent a decrease in productivity.

[0060] [Other configurations] Although the present invention has been specifically described above based on the embodiments thereof, the present invention is not limited to the above-described embodiments and can be modified in various ways within the scope of the invention as defined in the claims and their equivalents.

[0061] For example, in the above description, the control device 50 is configured to acquire the charge amount of the recording medium M itself, but this is not limiting. For example, the control device 50 may acquire the type of recording medium M as information related to the charge amount. In particular, a conversion table between the type of recording medium M and the charge amount is acquired in advance through experiments and stored in ROM. The control device 50 then calculates the cumulative charge amount using the type of recording medium M and the conversion table, and controls the operation of the head cleaning device 40.

[0062] It should be noted that the recording medium M is particularly susceptible to charging if it is PVC (polyvinyl chloride) or a plastic medium. Therefore, in this configuration, if the recording medium M is a plastic medium such as those described above, the conversion table is set so that the amount of charging is greater than for other media.

[0063] The control device 50 may also acquire the physical properties of the recording medium M as information related to the charge amount. The physical properties of the recording medium M include, for example, resistance and dielectric constant. Specifically, a conversion table between the physical properties of the recording medium M and the charge amount is acquired in advance through experiments and stored in ROM. A media sensor that measures the physical properties of the recording medium M is also provided in the paper feeder 10, and the measurement results are transmitted to the control device 50. The control device 50 then calculates the cumulative charge amount based on the physical properties of the recording medium M and the conversion table, and controls the operation of the head cleaning device 40.

[0064] Furthermore, if the static elimination performance of the static eliminator 22 is degraded, the amount of charge on the recording medium M remains relatively large. Therefore, the control device 50 may acquire the measurement result of the static elimination performance measuring device 22a as information regarding the amount of charge.

[0065] In the above description, the image forming apparatus 20 is provided with the static eliminator 22, but it is not preferable to increase the static eliminator effect on the recording medium M by, for example, providing a large number of static eliminators 22. For example, if the static eliminator 22 is an ionizer that blows ionized air toward the recording medium M, increasing the static elimination effect too much may cause the ink to thicken due to ozone or discharge products, which may cause problems with the inkjet head.

[0066] 4A and 4B, the amount (condition) of satellites adhering to the recording medium M changes depending on the charge amount of the recording medium M. The shape of the dots also changes depending on the charge amount of the recording medium M. Specifically, when the charge amount of the recording medium M is large, the shape of the dots becomes distorted. These changes can be detected by the control unit 50 from the reading results of the image reading unit 26. Therefore, the control device 50 may acquire the reading results of the image reading unit 26 as information related to the charge amount.

[0067] Furthermore, for example, in winter when the temperature is low, the recording medium M is more likely to become charged. Therefore, the control device 50 may acquire temperature information and / or humidity information as information related to the amount of charge. Note that the temperature information and humidity information are not limited to the state of the external environment, and may also include the temperature and humidity of the recording medium M.

[0068] Furthermore, a detection unit that detects mist adhering to the nozzle surface may be provided near each head unit, and the control device 50 may use the detection results, together with information related to the charge amount of the recording medium M, to control the cleaning operation of the head cleaning device 40. Specifically, the detection unit is a camera or a sensor. In this configuration, the control device 50 calculates the amount of mist adhering to the nozzle surface from the concentration obtained from the detection unit.

[0069] Furthermore, the control device 50 may use any one of the operating time, number of images formed, image forming conditions, and ink consumption amount of the inkjet recording device 1 in combination with information regarding the charge amount of the recording medium M to control the cleaning operation of the head cleaning device 40. Note that the image forming conditions specifically include the number of inkjet heads used, the image pattern, etc.

[0070] In addition, although the above example illustrates a case where the droplet ejection device is an inkjet recording device 1 that ejects ink, the present invention is not limited to this. That is, the liquid ejected by the droplet ejection device is not limited to ink, and may be any appropriate liquid such as a pretreatment agent.

[0071] In addition, in the above description, the inkjet recording apparatus 1 is configured to include the head cleaning device 40, but this is not limiting. The head cleaning device 40 may be a device separate from the inkjet recording apparatus 1, as long as it has the same functions and actions as those described above. Similarly, in the above description, the inkjet recording apparatus 1 is configured to include the control device 50, but this is not limiting. The control device 50 may be a device separate from the inkjet recording apparatus 1, as long as it has the same functions and actions as those described above.

[0072] In the above description, the head unit is moved to a position where the nozzle surface faces the head cleaning device 40 during the nozzle surface cleaning process, but this is not limiting. In other words, the cleaning means of the head cleaning device 40 may be moved to a position where it faces the nozzle surface.

[0073] Although the above describes an example in which a hard disk or a semiconductor nonvolatile memory is used as a computer-readable medium for the program according to the present invention, the present invention is not limited to this example. Other computer-readable media include portable recording media such as CD-ROMs. Furthermore, a carrier wave can also be used as a medium for providing the program data according to the present invention via a communication line. [Explanation of symbols]

[0074] 1. Inkjet recording device (droplet ejection device) 22 Static eliminator 22a Static elimination performance measuring device 23 Surface electrometer 24 Image forming unit 26 Image reading unit 40 Head cleaning device 50 Control device (control unit) M Recording medium

Claims

1. an image forming unit that records an image by ejecting droplets from nozzles of a droplet ejection head onto a conveyed recording medium; a head cleaning device that cleans the nozzle surface of the droplet ejection head; a control unit, The control unit controls a cleaning operation of the head cleaning device in accordance with information about the charge amount of the recording medium.

2. 2. The droplet ejection device according to claim 1, wherein the control unit controls the cleaning operation of the head cleaning device in accordance with the amount of charge on the recording medium before the image forming unit ejects droplets onto the recording medium.

3. a surface potential meter for measuring a surface potential of the recording medium on an upstream side of the image forming unit in a conveyance direction; The droplet ejection device according to claim 2 , further comprising: an acquisition unit that acquires the charge amount from the surface potential measured by the surface potential meter.

4. The droplet ejection device according to claim 1 , wherein the control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount set for each type of recording medium.

5. a media sensor for measuring physical properties of the recording medium; The droplet ejection device according to claim 1 , wherein the control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the measurement result of the media sensor.

6. a static elimination device that eliminates static from the recording medium; and a static elimination performance measuring device that measures the static elimination performance of the static elimination device, The droplet ejection device according to claim 1 , wherein the control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the measurement result of the static elimination performance measuring device.

7. an image reading unit that reads the image formed on the recording medium by the image forming unit; The droplet ejection device according to claim 1 , wherein the control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the read result of the image reading unit.

8. a measurement unit for measuring temperature information and / or humidity information, The droplet ejection device according to claim 1 , wherein the control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount corresponding to the measurement result of the measurement unit.

9. a detection unit that detects the amount of mist adhering to the nozzle surface, The droplet ejection device according to claim 1 , wherein the control unit controls the cleaning operation of the head cleaning device in accordance with information about the charge amount and the detection result of the detection unit.

10. The droplet ejection device according to claim 9 , wherein the detection unit is a camera or a sensor.

11. The droplet ejection device according to claim 1, wherein the control unit controls the cleaning operation of the head cleaning device in accordance with information regarding the charge amount and at least one of the operating time of the droplet ejection device, the number of images formed, the image forming conditions, and the amount of liquid consumed.

12. The droplet ejection device according to claim 1 , wherein the control unit controls a timing at which the head cleaning device cleans the nozzle surface as the cleaning operation.

13. The droplet ejection device according to claim 1 , wherein the control unit controls a strength at which the head cleaning device cleans the nozzle surface as the cleaning operation.

14. The droplet ejection device according to claim 1 , wherein the control unit controls the number of times the head cleaning device cleans the nozzle surface as the cleaning operation.

15. The head cleaning device includes a plurality of types of head cleaning means, The droplet ejection device according to claim 1 , wherein the control unit controls which of the plurality of types of head cleaning means is to be used for the cleaning operation.

16. an image forming unit that records an image by ejecting droplets from a droplet ejection head onto a conveyed recording medium; a head cleaning device that cleans the nozzle surface of the droplet ejection head, A head cleaning method comprising a control step of controlling a cleaning operation of the head cleaning device in accordance with an amount of charge on the recording medium.

17. an image forming unit that records an image by ejecting droplets from a droplet ejection head onto a conveyed recording medium; a head cleaning device that cleans the nozzle surface of the droplet ejection head; a program that functions as a control unit that controls the cleaning operation of the head cleaning device in accordance with the amount of charge on the recording medium;

Images